Field of the Invention
The present invention relates to an image processing method for improving an image quality of a shot image.
Description of the Related Art
In image pickup through an image pickup apparatus such as a camera, part of light incident on an image pickup optical system may be reflected by a surface of a lens and a member holding the lens and arrive at an imaging plane as unnecessary light. This unnecessary light appears as an unnecessary component such as a ghost and a flare in a shot image. When a diffractive optical element is used to correct longitudinal (axial) chromatic aberration and chromatic aberration of magnification, light from a high intensity object such as the sun outside an angle of view for the image shooting may be incident on the diffractive optical element, generating unnecessary light as an unnecessary component over the entire image.
Japanese Patent Laid-open No. 2008-54206 discloses a method of detecting any ghost based on a difference image indicating a difference between an image (in-focus image) when an image pickup optical system is in focus on an object and an image (defocus image) when the image pickup optical system is out of focus. However, the method disclosed in Japanese Patent Laid-open No. 2008-54206 requires image pickup to be performed a plurality of times and thus is not suitable for still image pickup and moving image pickup of a moving object.
Japanese Patent Laid-open No. 2011-205531 discloses a method of detecting any ghost based on comparison of a plurality of parallax images captured by a single-lens stereoscopic image pickup. The method disclosed in Japanese Patent Laid-open No. 2011-205531, which obtains a plurality of parallax images by single image pickup, is applicable to still image pickup and moving image pickup of a moving object.
However, the method disclosed in Japanese Patent Laid-open No. 2011-205531 detects any ghost by calculating a difference between a primary image and a secondary image, and thus has a degraded ghost detection effect when using parallax images captured at three viewpoints or more. Japanese Patent Laid-open No. 2011-205531 corrects an image shift caused by the parallax before detecting the ghost. In this case, a process such as extraction of a corresponding point can be applied to a focused object, but it is insufficient for a blurred object region and it is necessary to obtain detailed distance information (distance map) over an entire region of images from the image pickup apparatus to the object. On the other hand, when the ghost is to be detected without correcting the parallax difference, the parallax component as well as the ghost is detected and the parallax component and the unnecessary component (ghost component) cannot be separated from each other.
When a diffractive optical element is used in a telephoto lens to correct longitudinal (axial) chromatic aberration and chromatic aberration of magnification, light from a high intensity object such as the sun outside an angle of view for the image shooting may be incident on the diffractive optical element, generating unnecessary light over the entire image. This unnecessary light also appears as an unnecessary component in the shot image. Previously, a method of removing the unnecessary component by using digital image processing has been known.
Japanese Patent Laid-open Nos. 2011-205531 and 2014-171236 disclose a method of detecting any ghost based on comparison of a plurality of parallax images captured by a single-lens stereoscopic image pickup. The method disclosed in Japanese Patent Laid-open Nos. 2011-205531 and 2014-171236, which obtains a plurality of parallax images by single image pickup, is applicable to still image pickup and moving image pickup of a moving object.
In the method disclosed in Japanese Patent Laid-open No. 2011-205531, however, it is assumed that a parallax component is previously corrected and thus the ghost cannot be correctly detected when the parallax component still exists.
On the other hand, Japanese Patent Laid-open No. 2014-171236 discloses a method of detecting the ghost when the parallax component still exists. With respect to a distant view such as a landscape photograph which contains a small amount of parallax component, a low-pass filter can be applied to the parallax image to remove the parallax component. However, with respect to an image containing a large amount of parallax component such as an image focused on a close-distance object, application of the low-pass filter is insufficient to remove the parallax component. On the other hand, when the low-pass filter is strongly applied, the ghost to be detected decreases as well and it is difficult to appropriately detect the ghost.